Modified plastic bottle injection blow-molding apparatus and method

ABSTRACT

In an injection blow-molding process the preform is purposely formed as a smooth walled tube closed at one end and without any thread or other cap attachment configuration about the mouth of the preform. The preform is moved to the bottle mold which completely forms the cap attachment configuration with the bottle in the blow-molding step. A processing dome is also formed from the preform in the blow-molding step to provide means to transfer the bottle to the trimmer which removes the dome. By using the smooth walled preform (without threads or any other cap fastening features), the bottle mold may utilize only a portion of the vertical height of the preform for the bottle. Bottle molds for a variety of bottle volumes and heights may employ the same preform and preform injection mold. The smooth walled preform also permits bottle molds with a variety of mouth diameters to be employed with the same preform injection mold. Since the bottle mold provides the specific cap attachment configuration of the bottle such as threads or lugs, the same preform and preform injection mold may be employed for a variety of cap attachment configurations. By using a common preform only the bottle mold need be manufactured for each new bottle configuration thereby saving the cost of a dedicated preform injection mold and the cost of set-up time for the preform injection mold. The bottle molds can comprise sets of modular mold parts for exchangeability. For an injection blow-molding machine that is to be employed to manufacture several different bottle configurations on a batch basis each year the savings in tooling cost are considerable and the savings in set-up costs, processing time and minimum product rejects with the new process and apparatus can also be considerable. The new smooth-walled preform and preform injection mold apparatus and process is also applicable to the injection, stretch and blow-molding process for making bottles.

This is a continuation of application Ser. No. 08/313,368 filed on Sep.27, 1994, abandoned.

BACKGROUND OF THE INVENTION

The field of the invention pertains to the manufacture of plasticbottles and, in particular, to the processes of injection blow-moldingand injection, stretch and blow-molding wherein a bottle preform isfirst injection-molded and, as a second step, the preform is blow-moldedto the bottle shape. Between the first and second steps, the preform maybe stretched to the bottom of the bottle mold as an option for enhancedbottle material properties. This method is most commonly used for themanufacture of beverage bottles from polyethylene terepthalate (PET).

U.S. Pat. No. 4,603,831 discloses a process and apparatus for forming aninjection-molded preform followed by transport of the preform to abottle mold wherein the preform is blown into the bottle shape. U.S.Pat. No. 4,233,022 illustrates further the intermediate step ofstretching the preform to the bottom of the bottle mold prior to blowingthe preform to the bottle shape. The preform is stretched mechanicallyas shown.

U.S. Pat. No. 4,007,243 discloses the manufacture of bottles from ablown preform followed by a final blowing in a second final bottle mold.And, U.S. Pat. No. 3,940,231 discloses an intermediate step of thermaltreatment of the preform before the final blowing step to form thebottle.

U.S. Pat. No. 3,271,489 discloses a blow pin and neck finishingapparatus for forming the externally threaded neck of a bottle. In thispatent, the bottle is formed from an extruded parison directly enclosedby the bottle mold that forms the final bottle shape. Likewise, U.S.Pat. No. 3,769,394 is directed to the neck finishing of bottles blownfrom an extruded parison. The excess material above the threaded top ofthe bottle is sheared off as a part of the neck-finishing andthread-forming plunge of the apparatus into the parison trapped in themold.

U.S. Pat. No. 4,382,769 discloses a neck finishing blow pin and acrammer sleeve about the blow pin to pack in the parison in forming thethreaded top of the bottle. The crammer sleeve also acts to sever theparison above the top and remove the severed portion when the bottlemolds subsequently open. U.S. Pat. No. 4,390,338 is similarly directedto finishing the neck and threaded top of the bottle. The blow pineffects compaction of the plastic in the neck and top. A rotation collarand cutter collar remove the excess plastic from the top of the bottleas a part of the finishing process.

In the past, applicant has developed and used a modular mold system forsingle-step extruded parison bottle manufacture. The bottle moldscomprise a split stack of partial molds. For example, the bottle volumeportion, the neck and top portion, the processing dome portion, spacersas needed, and at the top of the bottle mold, a blow pin funnel arestacked. The processing dome formed above a bottle by the mold providesa means to transport the bottle to the trimmer. By means of the modularsystem, the overall mold height is maintained, the dome, spacer and blowpin funnel portions are standardized, and a wide variety of bottlesizes, shapes, neck and top configurations can be interchanged. A newbottle shape or top thread or other configuration can be added by merelymanufacturing only the new mold parts for the volume portion or the neckand top portion of the bottle. This modular system has substantiallyreduced the tooling cost and therefore the per bottle cost which makesfeasible relatively short-run bottle manufacture.

With a view toward expanding the advantages obtained above inmanufacturing one-step extrusion blow-molded bottles to the two-stepinjection blow-molded process and the three-step injection, stretch andblow-molded process, the applicant has invented the improvementsdisclosed below. Currently, in the injection step of both processes theinjection mold forms the thread or other cap fastening means and thecomplete sealing surface about the bottle mouth as a part of theinjected preform. After the preform is separated from the injectionmold, the preform is placed in the bottle mold. The bottle mold gripsthe preform about the thread to protect the thread from distortion andseals the preform against leakage of blowing air with a slightinterference fit just below the thread. Thus, the injection mold must becritically matched with the corresponding bottle mold. The interferencefit at the neck below the thread which provides the air seal can causedistortion of the plastic at the neck directly affecting the appearanceand usefulness of the bottle. A new thread or cap fastening means for abottle requires a new injection mold in addition to a new bottle mold.Also, a new height bottle requires a new injection mold in addition tothe new bottle mold.

Prior art injection blow molding can also require a different preformmold and bottle mold for materials differing in shrinkage rate. Thepossible requirement for a new injection mold as well as bottle moldalso arises from the carryover of exact dimensions from the preform tothe finished bottle, particularly with respect to the cap fasteningmeans.

SUMMARY OF THE INVENTION

The invention is directed to further modifications of the injectionblow-mold and injection, stretch and blow processes for plastic bottlemanufacture. The invention comprises injection molding a preform lackinga thread or other cap retention means and bottle-sealing surface at thetop of the preform. The preform is substantially cylindrically shapedwith a smooth circular wall extending to the mouth opening. The endopposite the mouth is closed. The invention is equally applicable toother preform cross-sections such as oblong. The preform is transferredon the injection mold core to the bottle mold wherein the bottle isblown. In blowing the bottle, the cap retention means and dome areformed and the sealing surface (sealing land) is partially formed at thelocation that will become the top of the bottle. The invention isequally applicable to the injection, stretch and blow process, however,typically means other than the injection mold core are used to transferthe preform.

In blowing the bottle, the neck, thread or cap fastening means, sealingland and processing dome are blown to shape with the bottle. The bottleis then removed from the bottle mold and transferred to a trimmingstation wherein the processing dome is removed and recycled. Thetrimming knife finalizes the smooth sealing surface about the bottlemouth. Thus, with the new process the preform does not require a smoothsealing surface or land at the preform mouth in the previous injectionmolding step. Therefore, the injection step is less critical and theentire height of the preform need not be used to form the finishedbottle.

The invention is specifically directed to relatively short-run bottleproduction but not limited thereto. The manufacturer who specializes insuch production must be able to minimize tooling and mold cost tominimize bottle production cost. With the above smooth wall shapedpreform, the same relatively simple and inexpensive injection mold canbe used to mold a single size preform capable for manufacture of a widevariety of bottle heights, volumes, mouth diameters and threaded orotherwise configured necks and tops.

Only the preform outside diameter is relatively fixed for the entirepanoply of bottle sizes, threaded tops and shapes. With a modularblow-mold system such as that previously developed for the extrusionblow-mold process by applicant but now applied to the bottle mold of theinjection blow-mold and injection, stretch and blow-molding processes,the cost of the injection mold can be significantly cut compared to aconventional injection mold with a threaded top and sealing land. In theprior art, in contrast, multiple injection molds are required fordiffering thread design or bottle height.

Since the bottle mold must have a thread protective top section in aconventional injection blow-mold system, two complicated top sectionsare provided in the tooling, one for the threaded preform injection moldand the other to protect the preform threads in the blowing step.Moreover, in the neck region just below the thread the blow-mold must becarefully fitted to prevent air leakage during blowing. This fit cancause distortion of the plastic and such distortion can cause bottlerejects.

In contrast, with applicant's new system changing a threaded top design,size of bottle mouth or bottle height only requires the bottle mold havethe new different thread configuration in the neck and top portion ofthe blow-mold. The preform injection mold need not be modified orremoved. Moreover, the seal against air leakage during blowing is wellabove the sealing land of the bottle and therefore any distortion in theplastic at the air seal is subsequently removed from the bottle andrecycled. Machine downtime for mold changeover is also decreased sinceonly the bottle mold need be changed.

With applicant's new system the preform cooling time and overall cycletime for the machine can be reduced. In a conventional process coolingthe injection mold formed threads of the cap fastening means isfrequently the portion of the preform making process which requires thelongest cooling time and sets the overall cycle time for thebottle-making process. With the smooth-walled preform of applicant'sprocess, the preform cooling time is reduced, the overall cycle time isreduced and, as an added benefit, less plastic is used because thethreads are blown and therefore have thinner plastic in the thread areaof the finished bottle. A lighter bottle and savings in material costare added benefits.

A further advantage results from the interchangeability of the bottlemold between injection blow-mold machines and extrusion blow-moldmachines. Utilizing applicant's modular blow-mold system for extrusionblow-molding with minor modifications to the split bottle mold, such asto the spacer and grip pieces of the modular bottle mold, the bottlemold can be used on either type of machine.

In the detailed description below, further advantages and capabilitiesarising from the invention are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in cross-section a new preform injection mold;

FIGS. 2a and 2b illustrate in cross-section the application forinjection blow-molding of the new same size preform on a core placedinside a bottle mold for a large bottle and for a small bottlerespectively;

FIGS. 3a and 3b illustrate schematically a bottle and dome afterejection from the bottle mold and just prior to dome removal;

FIGS. 4a, 4b and 4c illustrate in cross-section modified cores or aspacer sleeve positioned on the core to foreshorten the preforminjection mold;

FIGS. 5a and 5b illustrate the application in cross-section of the newpreform to a series of bottle sizes for the single machine injection,stretch and blow-molding process; and

FIGS. 6a and 6b illustrate the application in cross-section of the newpreform to a series of bottle sizes that can be stretched and blown witha single size of stored preform in a two machine alternative injection,stretch and blow-molding process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an injection mold 10 is shown schematically in cross-section.The mold 10 includes a two piece core 12, 13 extending into the moldfrom the top and an injection nozzle 20 with a gate 14 near the bottom16 of the mold. Below the core 12 is a larger aperture 18 to accommodatethe injection nozzle 20. Between the core 12, 13 and the mold 10 is acavity 22 that is smooth walled tubular-shaped with a closed end at thenozzle 20. Thus, injection of plastic into the cavity 22 creates apreform 24 having a smooth exterior and interior surface. The wallthickness of the plastic preform 24 may be changed by merely changing toa core 12, 13 with a slightly different external diameter. The preform24 may optionally include a small stripping lip 25 about the mouth. Themold 10 (whether a one piece or split mold) and core 12, 13 are simplerand less expensive to manufacture because no threads, lugs, bottlesealing surface or other configurations are incorporated in the preform24 at the injection molding step.

The core 12 with the preform 24 is released from the injection mold 10and moved to the bottle mold 26 as shown in two configurations in FIGS.2a and 2b. The bottle mold 26 comprises a stack of modular mold portionsfor each half-mold in the preferred mode, although a conventional moldone piece halves might be substituted for either configuration. Themodular mold stack comprises the lower volumetric bottle portion 28,neck and top portion 30, which may include threads or lugs or otherfeatures to enable a cap to fasten to a bottle, a processing domeportion 32, a grip portion 34 to tightly engage the preform 24 againstcore 12, 13 and core centralizer 36. The grip portion 34 height isspecified as needed to make the overall bottle mold height astandardized height. The corresponding portions in FIG. 2b aredesignated by primes.

The preform 24 on the core 12 extends almost to the bottom of the bottlemold cavity 38 maintaining a critical gap 39 as shown in eitherconfiguration of FIG. 2. Typically, the core 12 includes at least oneorifice (not shown) for blowing the preform 24 to the bottle shape. Theside-by-side comparison of FIG. 2a with FIG. 2b illustrates a relativelylarge bottle or a relatively small bottle and any size in between may beblown from the same preform 24. The lower volumetric bottle portion 28and the neck and top portion 30 determine the entire bottle shape, capfastening means and height. The height of the bottle determines theportion of the preform 24 that forms the bottle. The remaining portionof the preform 24 that forms the bottle processing dome 44 and is in thegrip portion 34 and core centralizer 36 above the bottle processing dome44 is subsequently trimmed from the bottle and recycled.

The preform 24 is tightly gripped by the grip portion 34 about the core12 to form a seal against leakage of gas as the bottle is blown.However, since this seal is above the processing or transfer dome,distortion of the plastic is not critical and the future top of thebottle located in the mold below the dome is not affected by anydistortion above the dome. Without concern for distortion of the bottlea better seal above the dome 44 can be achieved and cooling timedecreased.

For all of the bottle configurations, the bottom 38 of the bottle moldcavity is closely adjacent the closed end of the preform 24. Thisprovides for an even wall thickness around the bottle bottom. Inaddition, the bottle mouth within the neck and top portion 30 must be atleast but preferably is larger than the preform 24 outside diameter.However, a range of bottle mouth diameters exceeding the preform insidediameter can be made.

In blowing the preform 24 to bottle shape, the top of the bottle 42 anddome 44 are shaped by the configuration of the mold portions 30 and 32,respectively. As shown in FIGS. 3a and 3b, upon release of the newlyformed bottle 42 from the blow mold 26, the bottle 42 is moved to aseparate means to sever 45 the dome 44 from the bottle 42. The means tosever 45 comprises oppositely moving belts 46 and 48 which grip the dome44 and spin the bottle 42 against a knife 50 to sever the dome 44 andplastic thereabove thereby finishing the bottle and finishing thesealing land at the mouth of the bottle. The means to sever 45 is hereshown as the knife 50 and the oppositely moving belts 46 and 48, butother means such as a moving blade, or hot wire, could be advantageouslyemployed. Since the sealing land is formed partially in the blow moldand finished by the knife 50, there are no critical sealing dimensionsformed on the preform by the injection mold as distinguished from theprior art preform molds wherein critical dimensions for seals can causepremature mold wear and reject bottles. The severed dome 44 and plasticthereabove is reground for recycling.

By standardizing the overall height of the bottle mold 26, the height ofthe preform 24 is standardized at a height that in addition to thebottle height includes the dome portion 32, grip and spacer portion 34,and core centralizer 36. The preform injection mold 10 need not bechanged for changes in bottle top configuration, mouth of bottle, bottlevolume portion height or diameter. Only the core 12, 13 or portions ofthe core need be changed when or if required for changes in preform 24wall thickness that are then reflected in changes of wall thickness forthe final bottle.

With the same preform mold 10, a whole series of bottles differing insize, shape, mouth diameter, height, plastic material, top configurationand other parameters can be manufactured. The only limitations to bottlesize are those imposed by the maximum external size of the bottle mold26 (height and width) which controls maximum bottle height and diameter,respectively, and the preform mold cavity 22 height and diameter. Thepreform mold cavity 22 inside diameter controls the minimum mouthdiameter of the entire bottle series. Within a subset of identicalbottle heights, only the bottle mold volume portion 28 arid top portion30 need be tooled for a new bottle configuration. Materials of differingshrinkage rates do not require any change in preform mold because noneof the dimensions of the preform carry over to the final bottle andtherefore none of the dimensions of the preform are critical. Thus, thetooling cost and set-up time for relatively short-run production isminimized.

At times when only a lower segment of the preform is used to make ashorter bottle, in FIGS. 4a, 4b and 4c optional means forforeshortening, such as an enlarged three-piece core 51, cylindricalspacer sleeve 52 or enlarged two-piece core 53 can be positioned andretained on the core 12 in the preform injection mold 10. The enlargedcores 51 and 53 or sleeve 52 reduce the height of the preform 24 sealingoff the cavity 22 and therefore reduce the amount of plastic recycled inthe manufacture of relatively short bottles. Thus, in summary,regardless of bottle configuration, the bottom 38 of the bottle moldcavity is substantially fixed at the same elevation just below thebottom of the preform 24.

As is readily apparent a conventional extrusion blow mold (split bottlemold) can be used for the bottle mold of the new process. Only minormodifications to the mold such as changes in the air sealing locationneed be made. Moreover, these changes can be incorporated withoutpreventing the mold from being returned for use on a single stepextrusion blow mold machine. With applicant's modular bottle mold systemonly the spacer portion 36 and the grip portion 34 need be changed tomove a modular bottle mold back and forth between an extrusion blow moldmachine and an injection blow mold machine.

Further, and as illustrated in FIGS. 5a and 5b, a standardized preform24 can be applied to the injection, stretch and blow-molding process. Inthis embodiment, the injection molding step and blow-molding step areboth on the same machine; however, the preform 24 is transferred by aninsert 54 having a lip 56 that supports the preform 24 by the preformlip 25. The core 12 is retracted from the preform 24 prior to preformtransfer to the blow-mold 60. The insert 54 is both a part of theinjection mold 10, as shown by the dashed lines 58 in FIG. 1 and theblow-mold 60 as shown in FIGS. 5a and 5b. Therefore, a set of molds, onefor injection molding the preform 24 and one for stretching andblow-molding the bottle 42, are used in combination. Other sets of moldsare used to achieve other bottle configurations and sizes.

In FIG. 5a, a relatively large bottle mold 60 is illustrated. The mold60 includes a dome portion 62, top and threaded portion 64 and volumeportion 66. Above the lip 25 a plunger (not shown) is sized to fittightly about the preform 24 mouth to form a seal at 68; however, anydistortion of the plastic is not critical since the location is abovethe dome 62 and this portion of the blown bottle will be severed andrecycled after the bottle is ejected from the mold 60.

As shown, the bottom 70 of the volume portion 66 is spaced below thebottom 72 of the preform 24 a substantial distance to allow forstretching of the preform as indicated by the dashed line 74. Thepreform 24 is stretched by a downward plunger inserted (not shown) inthe preform until the bottom 72 of the preform is adjacent the bottom 70of the volume portion 66. Thus, the maximum depth of the volume portion66, below the standardized preform 24, is limited by the stretchabilityof the particular plastic material.

As shown in FIG. 5b, a considerably smaller bottle mold 60' is employedwith the same preform 24. In this application, the dome portion 62' andthe top and threaded portion 64' are located in the mold 60' at thelowest elevation practicable to permit the bottom 70' of the mold 60' tobe spaced from the unstretched bottom 72' of the preform 24 as much aspossible for the size of the bottle. Thus, the preform 24 may bestretched as indicated by the dashed line 74'.

FIGS. 5a and 5b illustrate the large and small extremes of bottles thatcan be formed using the standardized preform 24. In this embodiment,only the elevation of the insert 54 and lip 25 of the preform 24 remainconstant regardless of bottle mold 60.

With reference to FIGS. 6a and 6b, the injection molding step to createthe preform takes place on a separate machine from the stretching andblowing steps to create a bottle. In FIG. 6b, the corresponding portionsto FIG. 6a are designated by primes. The preforms are stored at roomtemperature in inventory. With a variety of potential bottleconfigurations, currently a variety of preform configurations are storedas inventory awaiting orders for particular bottle configurations.

When the preforms are to be formed into bottles, the preforms arereheated to the proper temperature for stretching and blowing, whereuponthe preforms are positioned in the bottle mold, stretched and blown.

In applying applicant's new preform 24, the need for a variety ofpreforms with cap fastening means in differing configurations iseliminated. The total number of preforms carried in inventory can besubstantially reduced by use of applicant's new preform lacking capfastening means.

The preform 24 is carried and positioned in the bottle mold 76 bycarrier 78 having thereon a shaped collar 80 that is inserted into themouth of the preform 24. The collar 80 may provide an interference fitwith the mouth of the preform 24 to provide a tight grip on the preformwhile taking the preform through the reheating step and into the bottlemold 76. Once in the bottle mold 76, the bottle mold forms a seal 82around the outside of the preform 24 adjacent the collar 80. As above,at the seal 82 distortion of the plastic is not critical to the finalbottle because this portion of the preform 24 will eventually be severedfrom the bottle and recycled.

In this embodiment, the elevation of the gripping and sealing location82 in the bottle mold 76 remains constant regardless of bottleconfiguration whether large 84 or small 84', top and threadconfiguration 86 or 86' and location of the processing dome 88 or 88'.

I claim:
 1. In an injection blow-molding machine for the manufacture ofplastic bottles comprising an injection mold and core to form a preformof plastic and a split bottle blow-mold to form a bottle by blowing agas into a preform placed therein,the improvement to the machinecomprising in combination a smooth walled generally tubular shapelacking any means to form cap fastening means and having at least oneclosed end, said shape formed by the injection mold and core, the bottleblow-mold comprising a bottle volume-forming portion, a dome-formingportion, and a cap attachment means-forming portion therebetween, and asleeve on the core, the sleeve being positioned to foreshorten thetubular shape in the injection mold.
 2. A set of molds for plasticbottle manufacture comprising a preform injection mold and at least onebottle mold,the injection mold comprising a smooth walled shape havingat least one closed end and a core in the injection mold, the core beingpositionable to form a smooth walled generally tubular shape, the coreand shape lacking any means to form cap fastening means and decreasingin diameter adjacent the one closed end to form the closed end of theshape, the bottle mold comprising a bottle volume-forming portion, a capattachment means-forming portion, and a dome-forming portion, and asleeve on the core, the sleeve being positioned to foreshorten thetubular shape in the injection mold.